I've only used an Android phone once for 5 min (my Mom got one for Christmas), but that was enough to run into Back button confusion. My assumption was that it

I've only used an Android phone once for 5 min (my Mom got one for Christmas), but that was enough to run into Back button confusion. My assumption was that it would take me up the stack, since when I entered the Mail program and navigated down, Back took me back up. But when I entered from some other place (like the settings app) then back wouldn't take me up to inboxes. I'm sure it would have made more sense if I realized it was a system-wide Back and not an app-only Back.